What are you plotting: * Independant variables? * Depenendant variables?

Determining the root cause: * A lot of times people on SMTnet can give you hints on the things that influence specific process defects. For instance, some processes, like wave soldering, can have several process controls that can influence a single defect. * There several tools [eg, fishbone charts, paretno charts, etc] can be used to sort through the issues of a problem. Do a net search to learn more about these tools. * Some people use designed experiments to sort through process controls to determine the level of influence of these factors. * There was a thread on root cause analysis a year or so ago. Search the fine SMTnet Archives.